Processor Clocking Control
Updated: October 19, 2012
Processor Clocking Control (PCC) is a feature for Windows Server 2008 R2 where the operating system and the underlying platform hardware cooperatively manage processor power management (PPM). With PCC, Windows continues to direct the processor performance according to the system workload and communicates the ideal amount of processor performance to another hardware entity in the system through a firmware-described interface.
This information applies to the following operating systems:
- Windows Server 2008 R2
- Windows 7
Typically, systems that use PCC are server platforms that have a separate management controller that is responsible for directing processor performance and power consumption. This controller is ultimately responsible for transitioning the processor to the specific performance state or throttle state that provides the requested level of processor performance. PCC allows the system manufacturer to innovate in related power management features because the underlying hardware platform can be made aware of specific operating system processor performance requirements.
When PCC is enabled, Windows is not in direct control of the processor’s performance state, but instead communicates its performance state preference to the underlying platform hardware. Typically, the platform should provide at least the requested amount of processor performance for the given interval. However, if the system is running under a power consumption budget, thermal condition, or other extraneous condition, the platform can temporarily violate the agreement and provide reduced performance. In this situation, the platform must notify Windows about the reduction in performance. The ability of the underlying platform hardware to notify Windows about power budgets, thermal conditions, or other extraneous conditions is a key benefit of PCC. It lets Windows adjust the processor performance algorithm and notify the administrator or user that the system processor performance is currently reduced.
PCC is supported only on Windows Server 2008 R2. It is not supported on Windows 7 client systems. PCC requires an out-of-band management device to change the processor performance and throttle states and is designed solely for server systems.